In a refrigeration cycle apparatus, such as an air-conditioning apparatus, when refrigerant is changed from R410A refrigerant, R4070 refrigerant, and other HFC mixed refrigerants having a lower boiling point than R134a refrigerant to R1234yf refrigerant, a need arises to increase a circulation amount of the refrigerant due to a low operating pressure of R1234yf refrigerant. As a result, a flow rate of the refrigerant flowing through a refrigerant circuit is increased to lead to an increase in pressure loss of the refrigerant and a reduction in operation efficiency of the refrigeration cycle apparatus. To address this problem, the refrigerant has been considered to be changed from R410A refrigerant, R4070 refrigerant, and other HFC mixed refrigerants to refrigerant having a property of causing disproportionation, such as R1123 refrigerant and a mixed refrigerant containing R1123 refrigerant. The refrigerant having the property of causing the disproportionation, such as R1123 refrigerant and the mixed refrigerant containing R1123 refrigerant, has a GWP equivalent to that of R1234yf refrigerant, and a higher operating pressure than R1234yf refrigerant. Consequently, in a case where the refrigerant is changed to the refrigerant having the property of causing the disproportionation, such as R1123 refrigerant and the mixed refrigerant containing R1123 refrigerant, the operation efficiency of the refrigeration cycle apparatus is enhanced to be higher than that of a case where the refrigerant is changed to R1234yf refrigerant.
Meanwhile, a related-art heat exchanger includes a main heat exchange unit including a plurality of first heat transfer pipes arranged side by side, a sub-heat exchange unit including a plurality of second heat transfer pipes arranged side by side, and a relay unit including a plurality of relay passages connecting the plurality of first heat transfer pipes and the plurality of second heat transfer pipes. The relay passages have inlets connected to the second heat transfer pipes, and outlets connected to the first heat transfer pipes. When the heat exchanger acts as an evaporator, refrigerant flows into the first heat transfer pipes from the second heat transfer pipes through the relay passages. When the heat exchanger acts as a condenser, the refrigerant flows into the second heat transfer pipes from the first heat transfer pipes through the relay passages (for example, see Patent Literature 1).